A current trend in the design of electrical systems is to modular system configurations wherein individual electrical units of the system are readily accessible and in some cases customer removable. The use of modular designs provides a number of different advantages. Manufacture and assembly is made simpler in that each unit can be manufactured and tested separately before being assembled in the complete system. Furthermore, if a removable unit becomes defective, it can be readily removed for repair and replaced with a working device. A typical multicomponent system of this type is a computing system in which data storage devices, processing hardware, power supplies and cooling fans are contained within a single support structure.
Although ease of removability of individual devices is facilitated using a modular configuration, the removal and replacement of a device usually requires the system to be closed down thus reducing the amount of time for which the system is available. Systems are now coming onto the market which allow for concurrent maintenance, i.e., provision is made to allow removal of a defective device whilst allowing continued operation of remaining elements of the system.
Taking the example of a disk file data storage system comprising removable disk files and associated power and cooling units, such systems are currently available which allow for the replacement of one or more of the disk files while maintaining operation of the remaining disk files. Furthermore EP-A-617 570 describes a data storage system including replaceable cooling and power assemblies; the system housing being configured to permit removal of these assemblies without the need to remove the disk files. Although ease of access to various subassemblies within a modular electronic system is a prerequisite to achieving the desired aim of concurrent maintainability, it is also necessary to build redundancy into the system so that removal of a defective device providing a system life support function, e.g., a power supply does not result in shortage of power to the system.
Concurrent maintenance of power supplies and/or signal paths between modules in a modular system can be achieved by creating independent removable dual paths. However this technique is not easy to apply where the paths cannot be separated, as in an electronics board or backplane in a storage subsystem, where it becomes necessary to remove sections of the backplane without disrupting the signals or power within the subsystem.
However, it is a continuing technical challenge to design modular electronic systems which provide ease of assembly and disassembly to give low manufacturing and service cost and at the same time achieve the high levels of fault tolerance which are becoming an increasingly important requirement in modem data storage systems.